GRAFT-HYBRIDS AND OTHER CHIMERAS 377 
the germ cells arise from the sub-epidermal layer. The seedlings of 
Gertnervcanum are also pure nightshade because, although this form 
consists of tomato tissue within, it is enveloped by two layers of night- 
shade cells. Similarly with proteus, which is a nightshade except for its 
two outer layers of tomato cells, the fruits resemble tomatoes and from 
theseed pure tomatoes have beenraised. Theother form, Awlreuterianum, 
fails to produce fruits. The chromosome numbers are 24 for the tomato 
and 72 for the nightshade. Ifa fusion of nuclei involving diploid numbers 
had occurred the cells of the supposed hybrids should contain 96 chromo- 
somes, but the only counts obtained by Winkler in the four chimeras 
were 24 and 72. Thus it appears that in each graft-symbiont the two 
kinds of tissue maintain their identity. Yet there is a combined effect 
on the morphological characters. The physiological interactions too 
are such as to cause reduced vigor. This effect is least noticeable in 
Kelreuterianwm which is sterile. The fifth new form, which Winkler 
Fie. 153.—Dtagram to show formation of adventitious buds arising at the point of 
union of the two graft-components A and B. a, represents a sectorial combination; b, a 
periclinal combination. (After Buder.) 
claims is a true graft-hybrid, was named Darwintanum. It appeared on 
one of the shoots from a decapitated graft. Winkler claims the chromo- 
some number of this form is 48 and that certain if not all of the tissues of 
this plant are composed of cells derived from the actual fusion of tomato 
with nightshade cells which involved nuclear fusion. If this is actually 
the case S. Darwinianum is a hybrid in the strict sense and the only one 
known to have been produced by vegetative means.: However, Baur 
points out that Winkler bases his claim for this number on the ground 
that he found 24 chromosomes in the pollen mother-cells which arise 
from the sub-epidermal layer. Baur thinks that Winkler’s interpretation 
is unwarranted. He believes it much more probable that S. Darwin- 
ianum is a periclinal chimera with a nightshade epidermis, then a sub- 
epidermal layer of tomato cells and the adjoining inner tissues of night- 
shade. Then the number found, 24, is the diploid number of the tomato 
and the reduction division, according to this explanation, is omitted in 
the tomato pollen mother-cells which, in this chimera, are bounded on 
both sides by nightshade tissues; or else it occurs at an unusually late 
stage in development. ‘I cannot admit,” says Baur, “that the exist- 
ence of real graft-hybrids in the strictest sense of the word is proven.” 
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